Multiple slit liquid thermal diffusion apparatus



Nov. 15, 1955 w. E SCOVILL MULTIPLE SLIT LIQUID THERMAL DIFFUSIONAPPARATUS 2 Sheets-Sheet 1 Filed May 20, 1953 INVENTOR.

WARNER E 5COVILL W ll TORNEYS NOV. 15, 1955 w v 2,723,759

MULTIPLE SLIT LIQUID THERMAL DIFFUSION APPARATUS Filed May 20, 1955 2Sheets-Sheet 2 INVENTOR. WARNER E. 5COV/LL HTTORNEYS United StatesPatent MULTIPLE SLIT LIQUID THERMAL DIFFUSION APPARATUS Warner E.Scovill, Lakewood, Ohio, assignor to The Stanillard Oil Company,Cleveland, Ohio, a corporation ofO io Application May 20, 1953, SerialNo. 356,284

4 Claims. 01. 210-52.s

The present invention relates to apparatus for separating dissimilarmaterials in a liquid mixture by continuous liquid thermal diffusion.More particularly, the invention is directed to apparatus having aplurality of liquid thermal diffusion separation chambers each dividedinto flow chambers by a liquid-permeable membrane.

The art of separating dissimilar materials in a liquid mixture bysubjecting the liquid to thermal diffusion dates back almost ninetyyears but remained largely a laboratory curiosity because of theextremely poor separations, from the standpoint of both quality andquantity, obtained. In recent years, however, interest has been revivedin liquid thermal diffusion as a means of separating dissimilarmaterials in a liquid mixture that are extremely difficult, if notimpossible, to separate by other means and to carry out such separationson a scale that would be commercially feasible.

U. S. Patents 2,541,069, 2,541,070 and 2,541,071, granted February 13,1951, to Jones and Hughes, describe a method of continuous liquidthermal diffusion and apparatus therefor wherein a thin stream of liquidmixture is introduced into a separation chamber defined by closelyspaced walls. The walls are relatively heated and cooled to maintain atemperature gradient across the thin stream of liquid in the chamber. Asa result of the heating of the portion of the liquid adjacent the wallhaving the relatively higher temperature, referred to as the hot wall orrelatively hot wall, and the cooling of the liquid adjacent the wallmaintained at the relatively lower temperature, referred to as the coldwall or relatively cold wall, a thermal circulation is set up whereinthe liquid adjacent the hot wall rises in the chamber and the liquidadjacent the cold wall descends. This thermal circulation brings about acountercurrent flow of liquid within the chamber. The thermal diffusionforce created by the temperature gradient across the liquid in thechamber operates to move one component of or in the liquid mixturetoward the cold wall and another toward the hot wall with the resultthat the two countercurrent streams in the chamber are each enriched byone component or the other. The molecular movement in the liquid acrossthe chamber and the gross movement of the liquid upwardly along the hotwall and downwardly along the cold wall due to thermal circulationcooperate to concentrate a liquid fraction enriched with a firstcomponent at the top of the chamber and another liquid fractionenrichedwith another component or impoverished in said first component at thebottom of the chamber. In carrying out the method and utilizing theapparatus described in these patents, it is important that the rate offeed of liquid into the chamber should not be such as to disturb thelaminar flow of the countercurrent streams in the chamber and promotephysical mixing thereof at the interface.

A further improvement in the liquid thermal diffusion art, involving theprovision of a liquid-permeable membrane intermediate the hot and coldwalls forming the chamber, has been proposed in application Serial No..1,

218,944 of Jones and Milberger, filed April 3, 1951, now Patent No.2,712,386, July 5, 1955 and assigned to the same assignee as the presentapplication. This membrane makes it possible to force the liquid intothe chamber at higher rates without interfering with the molecularmovement of the components to be separated from one side to another dueto the thermal diffusion eifect and, furthermore, without causingphysical mixing of the different fractions. The permeable membraneapparently functions as a barrier to gross flow between, or physicalintermixing of the liquidadjacent to the hot and cold walls whilepermitting the molecules in the liquid to pass freely through its poresand thus bring about a separation of the dissimilar components ormaterials in the initial liquid mixture'by continuous thermal diffusion.

The term liquid mixture is used broadly in the present application andis intended to refer to a liquid comprising a mixture of two or morecomponents in a liquid or liquefied state, to a solution of two or moredifferent materials as well as to liquid or liquefied solutioncontaining only one solute. Examples of such liquid mixtures arelubricating oils containing components of different viscosity indices,liquid mixtures of isomeric hydrocarbons and solutions thereof, fattyoils having glyceride esters of fatty acids of different molecularweights and saturation, liquid mixtures of hormones, viruses,antibiotics, etc., an azeotropic mixture of benzyl alcohol and ethyleneglycol, fish oil containing active vitamins and substances not havingvitamin activity, and the like.

The difference between the dissimilar components in or of a liquidmixture may be extremely minute. Thus, for example, they may have thesame empirical formula but differ slightly in structure or molecularweight.

The term separation as used hereinafter is intended to include not onlyseparation in the ordinary sense of the word but also rectification,concentration, enrichment, and purification. Thus, for example,separation into two or more fractions includes the separation ofpetroleum products in a liquid mixture thereof; the separation of benzylalcohol and ethylene glycol. from an azeotropic mixture of thesame intotwo fractions, one of which is richer in benzyl alcohol and the other ofwhich is richer in ethylene glycol than the starting mixture; theconcentration or enrichment of active vitamins in or from a mixture ofordinarily inseparable components, one of which may have vitaminactivity and the other not having such activity; the separation orconcentration of antibiotics and other biological products containingthe same; the separation or concentration of viruses; and the separationof vegetable oils, fats and waxes into components having differentdegrees of unsaturation, melting point and indices of refraction, theseparation of lubricating oil into fractions having different viscosityindices, and the like.

Generally the apparatus of the present invention comprises a series ofheat exchange elements having plane, vertical, smooth andliquid-impervious exterior walls forming a series of substantiallyvertical and uniformly narrow separation chambers between adjacent heatexchange elements. The chamber-forming walls of adjacent heat exchangeelements in the series are substantially coextensive with, parallel toand closely spaced from one another and means are provided forrelatively heating the separation chamber-forming walls of alternateheat exchange elements in the series and relatively cooling theseparation chamber-forming walls of the heat exchange elements betweensaid alternate heat exchange elements so that each separation chamber isformed by a relatively hot wall and a relatively cold wall. Therelatively hot walls of two adjacent separationchambers are.

Patented Nov. 15, 1955 formed by the exterior walls of a single heatexchange element and the relatively cold walls of two other adjacentseparation chambers are formed by the exterior walls of another singleheat exchange element. Liquidpermeable membranes are provided in theseparation chambers intermediate, spaced from and substantially parallelto the separation chamber-forming walls for dividing each separationchamber into parallel flow chambers so that each separation chambercontains one flow chamber adjacent a relatively hot wall and anotherflow chamber adjacent a relatively cold wall. The combined width of thefiow chambers in any one separation chamber may vary between about 0.01and about 0.15 inches, combined widths between 0.02 and 0.08 inchesbeing preferred. Inlet means are provided for continuously introducing aliquid mixture into at least one of the flow chambers. One outlet meansis provided for continuously withdrawing a first fraction of the liquidmixture from a fiow chamber in another of the series of separationchambers and another outlet means is provided for continuouslywithdrawing the second fraction of the liquid mixture from a flowchamber in still another of the series of the separation chambers.Further similar outlet means may be provided for withdrawing additionalfractions from other flow chambers. Conduits are provided forinterconnecting the flow chambers adjacent the relatively hot walls andthe fiow chambers adjacent the relatively cold walls in such a mannerthat liquid moving through flow chambers adjacent the hot walls willmove alternately upwardly and downwardly in alternate separationchambers and that liquid moving through the flow chambers adjacent thecold walls will alternately move downwardly and upwardly adjacent thecold walls. As a result, the direction of movement of liquid in the fiowchambers of each separation chamber is countercurrent. In alternateseparation chambers the flow is also in the same direction as thermalcirculation but in the other chambers between the alternate chambers thefiow is countercurrent to the direction of thermal circulation.

To facilitate an understanding of the apparatus of this invention and ofa typical flow pattern therethrough, reference is made to theaccompanying drawing wherein:

Figure l is a schematic flow diagram illustrating the manner in whichone embodiment of the apparatus of the invention can be used effectivelyand further illustrating diagrammatically the basic features of theapparatus;

Figure 2 is a schematic plan view of a thermal diffusion apparatusembodying the basic principles of this invention;

Figure 3 is an elevation in section taken on section line 33 of Figure2; and

Figure 4 is an end view in section taken on section line 4-4 of Figure2;

Figure 5 is a schematic plan view diagrammatically illustrating anotherembodiment of the apparatus of the invention; and

Figure 6 is a schematic flow diagram showing the manner in which theembodiment illustrated in Figure 5 may be employed.

In Figure l the heat exchange elements are diagrammatically representedby rectangles containing the letters H or C, each letter H signifying aheat exchange element that is relatively heated so that its verticalwalls will become hot walls, and each letter C signifying a heatexchange element that is relatively cooled so that its vertical wallswill become cold walls. The spaces between adjacent heat exchangeelements in Figure 1 signify thermal diffusion separation chambers. Thedashed lines signify liquid-permeable membranes which divide theseparation chamber into flow chambers. The solid lines with arrow headsindicate the direction of transfer of liquid from one flow chamber toanother and incidentally also the direction of gross flow of liquidwithin each flow chamber.

The apparatus illustrated by way of example in Figures 2, 3 and 4includes a plurality of adjacent heat exchange elements each comprisingat least one plane, vertical, liquid-impervious and chamber-forming wall10 of heat conductive material having a smooth exterior face 11. Thechamber-forming walls 10 of adjacent heat exchange elements aresubstantially parallel to one another and spaced apart to form aplurality of substantially parallel, vertical and uniformly narrowseparation chambers each divided, by a liquid-permeable membrane 12,into fiow chambers, five of which are designated, for convenience indescribing a typical operation of the apparatus, by reference numerals20, 22, 24, 26 and 28. The permeable membranes 12 may be convenientlymaintained between the opposed chamber-forming walls by gaskets 14 aswell as by other means described in more detail hereinafter.

Parallel to and adjacent the upper and lower ends of eachchamber-forming wall 11 there are provided passages, nine of which, forconvenience in describing the operation of the apparatus, are designatedby reference numerals 30 to 38. These passages communicate with the flowchamber immediately adjacent the wall in which the passages are locatedby means of one or more openings such as a groove 16 shown best inFigure 4. The other ends of the passages are interconnected, asillustrated best in Figure 2 and most completely in Figure 1. Means forrelatively heating alternate heat exchange elements are showndiagrammatically as comprising chambers 17 for receiving and discharginga heating medium such as steam, by way of lines 18 and 19. Heat exchangeelements that are relatively cooled are shown as comprising chambers 40supplied with a cooling medium by way of lines 41 and lines 42.

In the embodiments shown in Figures 2 to 4 the various heat exchangeelements of the apparatus are held together by tension bolts, or thelike, shown at 44.

The walls 10 may be of any suitable material, such as stainless steel,copper, aluminum, glass, brass or other alloys, that isliquid-impervious, heat conductive, and inert to any of the materialsbeing separated. The width of the separation chamber, exclusive of thethickness of the membrane, i. e., the combined width of the two flowchambers in each chamber, may be up to about 0.15 inch. Theoretically,there is no minimum combined width of flow chambers that would be toosmall, but as a practical matter, it is difficult to fabricate the wallsand the permeable membrane within sufliciently small tolerances toobtain clearances between both sides of the membrane and therespectively adjacent wall faces without making the combined width ofthe flow chambers at least about 0.01 inch. Combined widths of the orderof about 0.02 to about 0.06 inch are feasible structurally and preferredas optimum for most liquid thermal diflEusion operations. Excellentresults are obtainable, however, due to the much higher flow rates andseparations made possible by the membrane, when the combined width ofthe flow chambers is as great as about 0.08 inch.

Generally, the membrane must be permeable and reasonably inert withrespect to, and unaffected as to permeability by, all components of theliquid to be subjected to continuous thermal diffusion. It is preferredto make the membrane thin or a good conductor or both. The optimumthickness is necessarily a compromise between a minimum for therequisite heat conductivity and a maximum for strength. If necessary toavoid complete or partial blocking of the flow chambers, the membranemay be supported, on one or both sides, against lateral displacement byspacers or the like such as are described in application Serial No.271,182 of Jones and Milberger, filed February 12, 1952, and assigned tothe same assignee as the present application.

It has been found that membranes having a large number of very smallpores give better results than membranes having a smaller number oflarger pores, possibly because larger pores tend to permit gross flow ofthe liquid'as distinguished from movement of molecules or the likethrough the pores due to thermal diffusive forces.

The minimum size of the pores in the membrane is that suflicient topermit free movement, due to thermal diffusive forces, of all of themolecules or other particles in the liquid subjected to thermaldiffusive forces. There is no critical upper limit to the size of thepores but it is generally preferable that the average pore size be notappreciably greater than about 5 to microns on the average. Larger poresizes do not by any means render the thermal diffusion processinoperable. They are undesirable, however, because such larger poresizes promote gross flow of the liquid therethrough to an extent thatresults in a physical remixing of the enriched liquid fractions on thetwo sides of the membrane while adding nothing to the ease with whichthe molecules in the liquid may move across the separation chamber dueto the forces of thermal diffusion.

Papers such as duplicator paper, 16-, 20- and 24-lb. bond paper,andtracing paper have been found quite suitable as membrane material.Films of bentonite clay, thin sheets of porous stainless steel, and alaminate of fiber-glass material impregnated with a finely dividedfiller such as clay have also been found suitable.

The shape of the separation chamber-forming Walls has no appreciableeffect upon the degree of separation obtainable. The chambers formed bythe opposed walls may be long and narrow, as in the liquid thermaldiffusion apparatus described in U. S. Patent No. 2,541,069 whereinnomembrane is provided, or it may be square, trapezoidal or of any othershape.

It has been found that the degree of separation obtained with theapparatus of this invention is dependent primarily, all other conditionsbeing equal, upon the area of the permeable membrane. For structuralsimplicity, therefore, it has been found preferable to utilize flat andsubstantially square sheets of metal as the walls.

The openings such as opening 16 in the chamberforming walls and thepassages with which they communicate are preferably positioned andconstructed in such manner as to minimize turbulence in the flow of theliquid entering or leaving the flow chamber with which they communicate.Typical constructions that are desirable are described and illustratedin application Serial No. 273,737 of Jones, Seelbach and Frazier, and inapplications Serial Nos. 273,738 and 273,739 of Jones, all filedFebruary 27, 1952, and assigned to the same assignee as thisapplication.

In operation, the apparatus illustrated by way of example in Figures 2to 4 and further illustrated diagrammatically in Figure l, is filledwith the feed, i. e., the liquid mixture, and the heat exchange elementsare respectively heated and cooled, bearing in mind that the temperatureat the hot Walls should not be above the boiling or decomposition pointof the liquid or any of its components and that the temperature at thecold walls should not be below the freezing point or crystallizationtemperature of the liquid orany of its components, nor so low as torender it too viscous.

The liquid is then forced through the apparatus by means of pumps or thelike, as indicated in Figure 1, at a speed that is in excess of thenormal speed of thermal circulation referred to earlier. As shown inFigures 1 and 3, the liquid moving upwardly along the hot wall in flowchamber 22, for example, is transferred by way of passage 33, conduit 47and passage 35 to an adjacent flow chamber 24 for movement downwardlyalong the hot wall and from there is transferred, by way of passage 34and conduit 51, to another adjacent separation chamber for movementupwardly along a hot wall. The liquid moving downwardly along the coldwall in flow chamber 28, for example, is on the other hand, transferred,by way of passage 38, conduit 52 and passage 36, to the flow chamber 26in an adjacent separation chamber for movement upwardly along the coldwall and then, by way of passage 37, conduit 48 and passage 31, to theflow chamber 20 in another adjacent separation chamber for movementdownwardly along the cold wall, and so on. At one end of the series ofseparation chambers, as shown best in Figures 1-3, a portion of theliquid fraction in flow chamber 20 adjacent a cold wall is withdrawnfrom the apparatus by way of passage 30 and conduit 49 as product Po,the remainder being recycled by way of conduit 50 to flow chamber 22. Atthe other end of the series of separation chambers, as shown in Figure1, a portion of another liquid fraction in a flow chamber adjacent a hotwall is Withdrawn from the apparatus as product PH, the remainder beingrecycled to an adjacent flow chamber.

While these movements describe the gross flow of the liquid, it is to beborne in mind that due to the temperature gradient across eachseparation chamber there is also a molecular movement of materialsacross each separation chamber and through the membranes which resultsin a preference of some molecules for the flow chamber adjacent the hotwall and of other molecules for the flow chamber adjacent the cold wall.The molecules are then carried along with the gross flow of the liquidin the flow chamber and said liquid, being thus enriched in theparticular component represented by these molecules, becomes furtherenriched in successive passages through successive chambers until it iswithdrawn either from adjacent a hot wall at one end of the apparatus asproduct PH or at the other end of the apparatus as from adjacent a coldwall as product P0.

The apparatus illustrated in Figures 5 and 6, and its operation, isessentially similar to that shown in Figures 1 to 4 except that the heatexchange elements, indicated by H and C, are arranged differently andseveral alternate points of withdrawal for fractions PH and P0 areindicated at P'n and Pc.

The apparatus of this invention is to be distinguished from apparatusutilized in conducting separation methods based on osmosis and dialysisas well as from apparatus utilized in gaseous thermal diffusion andstatic liquid thermal diifusion methods.

In osmosis the separation or concentration of a solute in a solventdepends upon the semi-permeability of a membrane permeable to thesolvent and impermeable to the solute. Thus, for example, an aqueoussugar solution confined at least in part by a suitable membrane willbecome more concentrated due to the fact that the water will readilypass through the membrane whereas the sugar molecules cannot. In themethod of the present invention the membrane intermediate the hot andcold walls is equally permeable to all of the materials initiallyintroduced including the dissimilar materials to be separated.

In dialysis, a mixture of a colloid and a non-colloid can be separatedby the action of a semi-permeable membrane. Thus, for example, where anaqueous solution of both an ionized solute and a colloid is confined atleast in part by a suitable membrane, the colloid will remain while theionized solute will pass through because the membrane is permeable onlyto the latter.

In contrast to separation by osmosis or dialysis, separation by liquidthermal diffusion is dependent upon the existence of a temperaturegradient across a thin stream of the liquid and upon the ability ofdissimilar molecules therein to move from the hot side to the cold side,or vice versa, without any substantial restraint. The membrane used inthe method of this invention, which has been described heretofore, indetail, is pervious to all molecules in the liquid and is therefore abarrier only in the sense that it minimizes physical mixing of theliquids adjacent the hot and cold walls and hence permits forced flowpattern.

It is evident that many modifications in structure and flow pattern willbecome apparent to those skilled in the art upon reading thisdescription. It is to be understood that all such modifications areintended to be included within the scope of the invention as defined inthe accompanying claims.

I claim:

1. Liquid thermal diffusion apparatus comprising a series of heatexchange elements having plane, vertical, smooth and liquid-imperviousexterior walls, the exterior walls of adjacent heat exchange elements inthe series being substantially parallel to and closely spaced from oneanother to form a series of substantially vertical and uniformly narrowthermal diffusion separation chambers; means for relatively heating theseparation chamber-forming walls of alternate heat exchange elements inthe series of heat exchange elements and relatively cooling theseparation chamber-forming walls of the heat exchange elements betweensaid alternate heat exchange elements for providing a relatively hotwall and a relatively cold wall for each separation chamber, whereby therelatively hot walls of two adjacent separation chambers are formed bythe walls of a single heat exchange element and the relatively coldwalls of two other adjacent separation chambers are formed by the wallsof another single heat exchange element; liquidpermeable membranes inthe separation chambers intermediate and spaced from the separationchamber-forming walls for dividing each separation chamber into fiowchambers having upper and lower ends, one flow chamher in eachseparation chamber being adjacent a relatively hot wall and another fiowchamber in each separation chamber being adjacent a relatively coldwall; inlet means for introducing a liquid mixture into one of the flowchambers in said series of separation chambers; first outlet means forwithdrawing a first fraction of said liquid mixture from a flow chamberadjacent the relatively hot wall of another of the series of separationchambers; second outlet means for withdrawing a second fraction of saidliquid mixture from a fiow chamber adjacent a relatively cold wall ofstill another in the series of separation chambers; and meansinterconnecting the flow chambers of adjacent separation chambers formoving liquid, in alternate separation chambers, upwardly through theflow chambers adjacent the relatively hot wall and downwardly throughthe fiow chambers adjacent the cold walls, and for moving the liquid, inseparation chambers between said alternate separation chambers,downwardly through flow chambers adjacent the hot walls and upwardlythrough fiow chambers adjacent the cold walls.

2. Liquid thermal diffusion apparatus comprising a series ofsubstantially parallel heat exchange elements having plane, vertical,smooth and liquid-impervious exterior walls, the exterior walls ofadjacent heat exchange elements in the series being substantiallyparallel to and closely spaced from one another to form a series ofsubstantially vertical, parallel and uniformly narrow thermal diffusionseparation chambers; means for relatively heating the separationchamber-forming walls of alternate heat exchange elements in the seriesof heat exchange elements and relatively cooling the separationchamber-forming walls of the heat exchange elements between saidalternate heat exchange elements for providing a relatively hot wall anda relatively cold wall for each separation chamber, whereby therelatively hot walls of two adjacent separation chambers are formed bythe walls of a single heat exchange element and the relatively coldwalls of two other adjacent separation chambers are formed by the wallsof another single heat exchange element; liquid-permeable membranes inthe separation chambers intermediate and spaced from the separationchamber-forming walls for dividing each separation chamber into flowchambers having upper and lower ends, one flow chamber in eachseparation chamber being adjacent a relatively hot wall and another flowchamber in each separation chamber being adjacent a relatively coldwall; inlet means for introducing a liquid mixture into one of the flowchambers in said series of separation chambers; first outlet means forwithdrawing a first fraction of said liquid mixture from a flow chamberadjacent the relatively hot wall of another of the series of separationchambers; second outlet means for withdrawing a second fraction of saidliquid mixture from a flow chamber adjacent a relatively cold wall ofstill another in the series of separation chambers; and meansinterconnecting the flow chambers of adjacent separation chambers formoving liquid, in alternate separation chambers, upwardly through thefiow chambers adjacent the relatively hot wall and downwardly throughthe flow chambers adjacent the cold walls, and for moving the liquid, inseparation chambers between said alternate separation chambers,downwardly through flow chambers adjacent the hot walls and upwardlythrough flow chambers adjacent the cold Walls. 3. Liquid thermaldiffusion apparatus comprising a series of heat exchange elements havingplane, vertical, smooth and liquid-impervious exterior walls at an angleto one another, the exterior walls of adjacent heat exchange elements inthe series being substantially parallel to and closely spaced from oneanother to form a series of substantially vertical and uniformly narrowthermal diffusion separation chambers disposed radially of a verticalreference axis; means for relatively heating the separationchamber-forming walls of alternate heat exchange elements in the seriesof the heat exchange elements and relatively cooling the separationchamberforming walls of the heat exchange elements between saidalternate heat exchange elements for providing a relatively hot wall anda relatively cold wall for each separation chamber, whereby therelatively hot walls of two adjacent separation chambers are formed bythe walls of a single heat exchange element and the relatively coldwalls of two other adjacent separation chambers are formed by the wallsof another single heat exchange element; liquidpermeable membranes inthe separation chambers intermediate and spaced from the separationchamber-forming walls for dividing each separation chamber into flowchambers having upper and lower ends, one flow chamber in eachseparation chamber being adjacent a relatively hot wall and another flowchamber in each separation chamber being adjacent a relatively coldwall; inlet means for introducing a liquid mixture into one of the flowchambers in said series of separation chambers; first outlet means forwithdrawing a first fraction of said liquid mixture from a flow chamberadjacent the relatively hot wall of another of the series of separationchambers; second outlet means for withdrawing a second fraction of saidliquid mixture from a flow chamber adjacent a relatively cold wall ofstill another in the series of separation chambers; and meansinterconnecting the flow chambers of adjacent separation chambers formoving liquid, in alternate separation chambers, upwardly through theflow chambers adjacent the relatively hot wall and downwardly throughthe flow chambers adjacent the cold walls, and for moving the liquid, inseparation chambers between said alternate separation chambers,downwardly through flow chambers adjacent the hot walls and upwardlythrough flow chambers adjacent the cold walls.

4. Liquid thermal diffusion apparatus comprising a series of heatexchange elements having plane, vertical, smooth and liquid-imperviousexterior walls, the exterior walls of adjacent heat exchange elements inthe series being substantially parallel to and closely spaced from oneanother to form a series of substantially vertical and uniformly narrowthermal diffusion separation chambers; means for relatively heating theseparation chamberforming walls of alternate heat exchange elements inthe series of the heat exchange elements and relatively cooling theseparation chamber-forming walls of the heat exchange elements betweensaid alternate heat exchange elements for providing a relatively hotwall and 9 a relatively cold wall for each separation chamber, wherebythe relatively hot walls of two adjacent separation chambers are formedby the walls of a single heat exchange element and the relatively coldwalls of two other adjacent separation chambers are formed by the wallsof another single heat exchange element; liquid-permeable membranes inthe separation chambers intermediate and spaced from the separationchamber-forming walls for dividing each separation chamber into flowchambers having upper and lower ends, one flow chamber in eachseparation chamber being adjacent a relatively hot wall and another flowchamber in each separation chamber being adjacent a relatively coldwall; inlet means for introducing a liquid mixture into one of the flowchambers in an intermediate separation chamber of said series ofseparation chambers; first outlet means for withdrawing a first fractionof said liquid mixture from a flow chamber adjacent the relatively hotwall of a separation chamber at one end of the series of separationchambers; second outlet means for withdrawing a second fraction of saidliquid mixture from a flow chamber adjacent a relatively cold wall of aseparation chamber at the other end of the series of separationchambers; and means interconnecting the flow chambers of adjacentseparation chambers for moving liquid, in alternate separation chambers,upwardly through the flow chambers adjacent the relatively hot wall anddownwardly through the flow chambers adjacent the cold walls, and formoving the liquid, in separation chambers between said alternateseparation chambers, downwardly through flow chambers adjacent the hotwalls and upwardly through flow chambers adjacent the cold walls.

References Cited in the file of this patent UNITED STATES PATENTS2,158,238 Hvid May 16, 1939 2,330,672 Braak Sept. 28, 1943 2,386,826Wallach et al. Oct. 16, 1945 2,405,456 Signer Aug. 6, 1946 2,541,069Jones et al. Feb. 13, 1951 2,541,071 Jones et al. Feb. 13, 19512,585,244 Hanson Feb. 12, 1952

1. LIQUID THERMAL DIFFUSION APPARATUS COMPRISING A SERIES OF HEATEXCHANGE ELEMENTS HAVING PLANE, VERTICAL, SMOOTH AND LIQUID-IMPERVIOUSEXTERIOR WALLS, THE EXTERIOR WALLS OF ADJACENT HEAT EXCHANGE ELEMENTS INTHE SERIES BEING SUBSTANTIALLY PARALLEL TO AND CLOSELY SPACED FROM ONEANOTHER TO TO FORM A SERIES OF SUBSTANTIALLY VERTICAL AND UNIFORMLYNARROW THERMAL DIFFUSION SEPARATION CHAMBERS; MEANS FOR RELATIVELYHEATING THE SEPARATION CHAMBER-FORMING WALLS OF ALTERNATE HEAT EXCHAGEELEMENTS IN THE SERIES OF HEAT EXCHANGE ELEMENTS AND RELATIVELY COOLINGTHE SEPARATION CHAMBER-FORMING WALLS OF THE HEAT EXCHANGE ELEMENTSBETWEEN SAID ALTERNATE HEAT EXCHANGE ELEMENTS FOR PROVIDING A RELATIVELYHOT WALL AND A RELATIVELY COLD WALL FOR EACH SEPARATION CHAMBER, WHEREBYTHE RELATIVELY HOT WALLS OF TWO ADJACENT SEPARATION CHAMBERS ARE FORMEDBY THE WALLS OF A SINGLE HEAT EXCHANGE ELEMENT AND THE RELATIVELY COLDWALLS OF TWO OTHER ADJACENT SEPARATION CHAMBER ARE FORMED BY THE WALLSOF ANOTHER SINGLE HEAT EXCHANGE ELEMENT; LIQUIDPERMEABLE MEMBRANES INTHE SEPARATION CHAMBERS INTERMEDIATE AND SPACED FROM THE SEPARATIONCHAMBER-FORMING WALLS FOR DIVIDING EACH SEPARATION CHAMBER INTO FLOWCHAMBERS HAVING UPPER AND LOWER ENDS, ONE FLOW CHAMBER IN EACHSEPARATION CHAMBER BEING ADJACENT A RELATIVELY HOT WALL AND ANOTHER FLOWCHAMBER IN EACH SEPARATION CHAMBER BEING ADJACENT A RELATIVELY COLDWALL; INLET MEANS FOR INTRODUCING A LIQUID MIXTURE INTO ONE OF THE FLOWCHAMBERS IN SAID SERIES OF SEPARATION CHAMBERS; FIRST OUTLET MEANS FORWITHDRAWING A FIRST FRACTION OF SAID LIQUID MIXTURE FROM A FLOW CHAMBERADJACENT THE RELATIVELY HOT WALL OF ANOTHER OF THE SERIES OF SEPARATIONCHAMBERS; SECOND OUTLET MEANS FOR WITHDRAWING A SECOND FRACTION OF SAIDLIQUID MIXTURE FROM A FLOW CHAMBER ADJACENT A RELATIVELY COLD WALL OFSTILL ANOTHER IN THE SERIES OF SEPARATION CHAMBERS; AND MEANSINTERCONNECTING THE FLOW CHAMBERS OF ADJACENT SEPARATION CHAMBERS FORMOVING LIQUID, IN ALTERNATE SEPARATION CHAMBERS, UPWARDLY THROUGH THEFLOW CHAMBERS ADAJCENT THE RELATIVELY HOT WALL AND DOWNWARDLY THROUGHTHE FLOW CHAMBERS ADJACENT THE COLD WALLS, AND FOR MOVING THE LIQUID, INSEPARATION CHAMBERS BETWEEN SAID ALTERNATE SEPARATION CHAMBERS,DOWNWARDLY THROUGH FLOW CHAMBERS ADJACENT THE HOT WALLS AND UPWARDLYTHROUGH CHAMBERS ADJACENT THE THE COLD WALLS.